Ejections of magnetic structures above a spherical wedge driven by a convective dynamo with differential rotation

Warnecke Joern, joern@nordita.org, Nordita, Sweden
Kapyla Petri, Department of Physics, Helsinki University
Mantere Maarit, Department of Physics, Helsinki University
Brandenburg Axel, Nordita

Abstract
Observations show that the Sun sheds mass through wisted magnetic flux configurations, like Coronal Mass Ejections (CMEs). Conventionally, CMEs are modeled by adopting a given distribution of magnetic flux at the solar surface and letting it evolve by shearing and twisting the magnetic field at its footpoints at the surface. Of course, ultimately such velocity and magnetic field patterns must come from a realistic simulation of the Sun's convection zone, where the field is generated by dynamo action. Therefore a unified treatment of convection zone and CMEs is needed. We combine a convectively driven dynamo in a spherical shell with a nearly isothermal density-stratified exterior that mimics aspects of a stellar corona to study the emergence and ejections of magnetic field structures. This approach is an extension of earlier models where we employed forced turbulence simulations to generate magnetic fields. A spherical wedge is used which consists of a convection zone and a corona up to more than twice the radius of the sphere. The wedge contains a quarter of the azimuthal extent of the sphere and 150° in latitude. The magnetic field is self-consistently generated by the turbulent motions due to convection underneath the surface. Magnetic fields are found to emerge at the surface and are ejected to the coronal part of the domain. These ejections occur in irregular intervals and are weaker than in earlier work. We tentatively associate these events with coronal mass ejections on the Sun.